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Morning All! I need some advise please, a bit stumped at the moment. I drove from Reading to the Nurburgring last Thursday, about 380 miles. After about 320 miles into the journey, in Belgium, the low coolant level alarm/alert went off. I pulled over when it was safe to do so after a few miles. The alarm went off when going downhill on a piece of motorway which was restricted to one lane with no safe place to pull over. I noticed in these nerve-wracking few miles that the temperature gauge moved up and down but mainly stayed down around 60-65C. On uphill sections the alarm reset and the flashing thermometer stopped flashing, leading me to believe there must at least have been some liquid in the expansion tank.
Anyway, when I stopped there was still some coolant in the tank but it was very low. I topped it up with about 0.75 litres of water and set off again. On arrival at the 'Ring (about 60 miles on) I let the car cool right down before adding maybe another 0.25 litres, to slightly over the max line on the tank. Skip forward to Sunday, the first time I used the car since Thursday - left Germany for home. On arrival at the Channel Tunnel, after a 270 odd mile drive, the coolant alarm went off again. I let it cool for an hour or so and topped up again with about 0.75 litres. Drove home, just before I arrived, after about 105 miles, it went off again. Let it cool overnight, added about 0.75 litres to get it to max. So on this last run it consumed the water much faster, although I was driving faster. Since then I have tried to find where the liquid is going. There is no sign of a leak anywhere, that I can see. I don't think the head gasket has gone, there's no mayonnaise-like gunge on the oil filler cap, no bubbles in the expansion tank, no apparent overheating. When I release the pressure cap after a drive there is the usual pressure equalisation, but after a minute or so of running there is no more pressure build up. The engine is still running beautifully so I'm leaning towards an external leak but just cannot see where it is. Any pointers gratefully received!!
Edited to state that the car has done 163600 miles, without missing a beat. Cambelt/water pump change done at 123000 miles.

Thanks Chema. Further to my original post, I took the car out just now for a two minute drive, from cold. There was a significant release of pressure when I removed the cap on the expansion tank. Did the same again straight away, same result. Everything I’ve read suggests head gasket failure with that kind of pressure build up. Hope I’m wrong, any more thoughts?

Don't worry too much. There is a test it can be done at the expansion cap to detect the presence of combustion fumes, but I won't go that far yet. I was in a similar situation after hitting a deer in the motorway amd having to change the bumper and the aircon condenser. Car started to loose coolant after a month or so, and I though the radiator was damaged. After pressure testing the circuit, and finding it was holding pressure, the cap was replaced and the car is running fine since them.

Because these tools are not cheap, why don't you try to replace the cap first, it's cheap.

I bought and fitted a new cap and took it down the M4 for an 80 mile trip - still losing water I’m afraid, out of the pressure release overflow. I did notice some bubbles coming into the tank from the bottom hose, not loads, just a glug every 4 or 5 seconds. Have taken car into my local VW/Audi specialist, he thinks it could be the water pump. He pressure tested the system and found no other leaks. Will report back.

Yes Rob, I’m of the same opinion. The man who’s working on the car said HG failures on this engine are very rare - he’s only seen one in all his years working on them. So it’s worth testing or checking everything first I think, just in case.....

We see this all the time, it usually leads to the car being scrapped, it is classic PD 8v head gasket failure. VW specify that the head must not be "reworked" as it removes the Hot Isostatic Pressing heat treatment and this will lead to porosity and premature failure, we just fit a new AMC head or refuse to do the job.

Dark was that day when Diesel conceived his grim engine that begot you, vile invention, more vicious, more criminal than the camera even, metallic monstrosity, bale and bane of our culture, chief woe of our Commonweal. How dare the Law prohibit hashish and heroin yet license your use, who inflate all weak inferior egos? Their addicts only do harm to their own lives: you poison the lungs of the innocent, your din dithers the peaceful, and on choked roads hundreds must daily die by chance-medley. Nimble technicians, surely you should hang your heads in shame. Your wit works mighty wonders, has landed men on the Moon, replaced brains by computers, and can smithy a "smart" bomb. It is a crying scandal that you cannot take the time or be bothered to build us, what sanity knows we need, an odorless and noiseless staid little electric brougham.

Thanks for the replies. I picked the car up this afternoon. It turns out that there was a selection of cooling system faults! Hopefully now fixed. There was a slight weep from the water pump, unseen by me. The thermostat was inoperative, I believe the mechanic said it was stuck in the closed position. He did a fault code scan which revealed that the temperature sender was faulty. The cam belt and water pump were replaced. The old pump was OK but was replaced as a matter of course. Genuine Audi parts used throughout. Tested for 15 miles or so, all seems fine, nice to have a temperature gauge which works properly again, I hadn’t realised how ‘vague’ it had become. The acid test comes tomorrow with a drive to Devon via Oxford and back. Large water supply will be ready just in case.

Looks like the head gasket, still pumping water out of expansion tank. Is there a guide somewhere here on head removal & replacement? I’d like to have a go myself. I’ve rebuilt loads of V8 petrol and motorcycle engines so I’m not afraid to do it myself, Diesel engines and fuel injection systems do make me a little nervous though. Any help or tips (and links to a manual!) would be massively appreciated. The car is a 2002 Tdi 130 Sport Avant, Manual box, AVF engine. Cheers.

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